This collection of images spans the shallowest marine environments including beach, lagoon-bay with all the associated environments such as sand-spits and barrier-bars, tidal flats, estuaries and coastal dunes. Where possible I have paired modern analogues with ancient examples.
The Atlas, as are all blogs, is a publication. If you use the images, please acknowledge their source (it is the polite, and professional thing to do).
This image and the one below show the Tairua estuary (Coromandel, NZ) at two stages of an ebb tide, with gradual exposure of a attached and mid channel sand bars. The whitish patches on the middle bar are shell banks. The main tidal channel is bottom center (out of the picture). The estuary in the distance has broad swaths of mangroves and seagrasses.A mix of wavy-crested, lunate and cuspate ripples developed during an ebb tide on the exposed platform margin to an ebb tidal delta – the main channel exits oceanward to the left. Some larger subaqueous dunes near the channel margin. Raglan, N.Z.The estuary on the south side of Galway Bay, County Clare, Ireland, near New Quay. The boulder-cobble beach consists almost entirely of Burrens limestone (Carboniferous). Left view from Abbot Hill.Mudflats and algae, Kinvara, at the head of the estuary, south side Galway Bay.Karst in Burren Limestone at Flaggy Shore, New Quay, County Clare, has been accentuated by salt corrosion and mechanical erosion. It is overlain by boulders of locally derived Carboniferous limestoneBoulder storm ridge at Black Head, County Clare – the heart of the Burrens. All boulders are locally derived Carboniferous limestone
Three images of potholes in Burren Limestone, Flaggy Shore, County Clare. Pebbles and cobbles become trapped in bedrock depressions that are gradually enlarged and deepened by the abrasive action of the clast moved and jostled by waves.
Large, 2D subaqueous dunes, intertidal Minas Basin, Fundy Bay. Late stage ebb ripples in the troughs.Reactivated 2D dunes with superposed ebb tide ripples, Minas Basin, Fundy BayMultiple 3D subaqueous dune sets that migrated left, and superposed ripples, intertidal, Minas Basin, Fundy Bay.Large 2D and 3D dunes, and superposed run-off ripple sets, Minas Basin Fundy BayLarge 3D dunes; primary migration to the right. Ripples developed during the later stages of ebb tidal flow. Minas Basin Fundy BayEbb tide run-off & reactivation of 3D dunes with superposed ripples. Minas Basin Fundy BaySandy tidal flat, straight- to wavy-crested ripples, locally bifurcated; flow to the right. Minas Basin, Fundy BayShallow subtidal to intertidal, 2D subaqueous dunes in sandstone, Rowatt Fm, Belcher Islands (Aphebian, about 2 billion years old). Amplitude is 12-15 cm. Paleoflow was to the right. Hammer for scale.Cross-sectional view of 2D subaqueous, intertidal dunes, showing complex migrating dune-formed crossbedding, and dune reactivation, Rowatt Fm, Belcher Islands (Aphebian, about 2 billion years old). The sands are mixed siliciclastic-carbonate (dolomite).Proterozoic tidal bedforms – reactivated subaqueous dunes (mid image), possible herringbone crossbeds, and smaller ripples. Also evidence for beachrock in the lower broken bed. Rowatt Fm, Belcher Islands (about 2 billion years old). Lens cap bottom right.Paleocene, straight crested and bifurcating wave ripples (approximately equal stoss and lee faces on each ripple), Expedition Fm, Axel Heiberg Is;and, Canadian ArcticBedding exposure of straight-crested current ripples in Paleocene intertidal deposits, Expedition Fm, Axel Heiberg Island, Canadian Arctic. Hammer left-mid image.Flood tide ripples over-ridden by smaller ebb tide ripples sets, creating an interference pattern, typical of tidal environments. Minas Basin, Fundy BayTidal flat, interference ripples, Minas Basin Fundy BayInterference ripples in Proterozoic tidal flat facies, Belcher IslandsSalt marsh deposits, representing at least three cycles of shoreline-marsh advance and retreat. Each contains abundant root remains including wood from coastal shrubs encased in carbonaceous mud and sandy mud. The white sheen is salt.Panoramic view of salt marsh cycles, Minas Basin, Fundy Bay. Modern vegetation includes salt-tolerant sedges.Salt marsh, sedges and small mangroves being transgressed and overlain by tidal flat muddy sands as the shoreline moves landward. This is a modern example of a ravinement surface. Whitford, south AucklandEroded salt marsh deposits, transgressed by sandy tidal flat – beach. The erosion surface is a modern, active ravinement surface. Galveston, Texas. The carbonaceous, muddy marsh deposits contain abundant root casts and evacuated burrows.Small meandering tidal channel in very muddy estuarine tidal flats, Whitford Estuary, south Auckland. Bank failure is common. The surface is littered with the gastropod Amphibola crenata and crustacean burrows.Mangroves dominate this estuarine channel-tidal flat system. The channel is mud-bound, about 1.5 m to 2 m deep and 5 m to 6 m wide, with margins stabilised by the tangle of roots. Tidal flood waters cover the vegetated flats to depths of only a few centimetres. Each tidal cycle replenishes the supply of food and nutrients to the vegetation and the local invertebrate fauna. Whitford estuary, south Auckland.Paleocene estuarine or tidal flat deposits containing lenticular ripple bedding (light coloured sandstone in upper half of image) encased in and draped by dark grey, carbonaceous mudstone laminae. Ripple migration was to the left. Ellesmere Island. Coin diameter is 24 mm.Paleocene tidal bedding (mostly lenticular and wavy bedding) interfingering with lagoon and marsh. Eureka Sound Group, Ellesmere IslandPaleocene tidal bedding interfingering with marsh-lagoon-bay sediment. On the right, the thicker sandstones may represent storm washovers into the bay. Eureka Sound Group, Ellesmere IslandCoarsening- and sandier-upward bay or lagoon subtidal to beach succession, cut by small tidal channels (lenticular sandstones at base of outcrop). Part of a cyclical succession of shallow shelf-shoreface facies. Eocene, Eureka Sound Group, Ellesmere Island.Ebb tidal delta at the mouth of Waikato River, south Auckland. The seaward margin of the delta is marked by the breaking waves.The ebb tidal delta outboard of Raglan Harbour, N.Z. and explanatory diagramTidal inlet standing waves (antidunes) in an outgoing tide, Mangawhai Heads, north Auckland. The antidunes migrate upcurrent (against the current) and gradually build until they break, subsequently reforming.Proterozoic tidal channel – inlet trough crossbeds; this outcrop gives a 3-dimensional view of individual sets. Paleoflow was into the image. Rowatt Fm. Belcher Islands.Paleocene subaqueous dunes up to 2m amplitude, in tidal inlet-delta, overlain by thin tidal flat-salt marsh deposits. Scattered pebble lags at the base of the channel subaqueous dune crossbeds Expedition Fm, Axel Heiberg Island, Canadian ArcticLarge within-channel dunes in a tidal inlet associated with a sand spit facies; the spits and bars were attached to (paleotopographic) headlands across an unconformity eroded into Ordovician carbonates. Paleocene, Eureka Sound Group, Ellesmere Island.The unconformity (arrows) between Ordovician carbonates and Paleocene estuarine-tidal channel-spit facies that onlap an irregular, karst paleotopography. Eureka Sound Group, Ellesmere Island.An annotated view of the karst and erosional relief on a subaerial unconformity developed on Ordovician carbonates, onlapped by Paleocene estuarine and shallow shelf deposits. Ellesmere Island.Beach cusps, Long beach, Vancouver Island, formed during a prolonged period of fine weather. The next storm will erode the cusps and redistribute the sand. Typical beach stratification in an eroded berm; primarily laminated sets with low-angle truncations, parallel, or slightly inclined to the beach face.Gravel bar formed at the intersection of a high energy West coast New Zealand beach, and the Tangahoe River mouthLenticular and flaser bedding in Late Pleistocene intertidal – estuarine deposits. The sand ripples are dark grey hues, the mudstones pale grey. Manukau Harbour, west Auckland. Coin diameter at lower center is 25 mm.Coastal dunes, Galveston coast, Texas. A storm washover (upper left) encroached and interfingers with lagoonal deposits.Sand washover fan breaching coastal dunes and interfingering with lagoonal – marsh deposits, Galveston coast, TexasPaleocene washover-fan sandstone associated with barrier island and tidal inlets (see images above from the same formation). The sands overlie and interfinger with thin coaly and carbonaceous marsh-lagoon deposits. Expedition Fm, Axel Heiberg Island, Canadian Arctic. Person for scale in the image center.A succession of storm deposits associated with an upper tidal flat, each layer consisting of ripped up muds. Clasts in the thick, upper bed have retained their original laminations and locally small ripple crossbeds. Other structures include current ripples, desiccation cracks, and flaser bedding. Rowatt Fm, Belcher Islands. Proterozoic.Desiccation cracks and polygons in salt marsh muds, Kaiua, south Auckland, NZ. Salt crystals have precipitated on some parts of the surface because of prolonged exposure between flooding by spring (king) tides.Desiccated, curled, algal mats from a salt marsh near Galveston Texas. The mats are easily disturbed during high or storm tides.Proterozoic supratidal desiccation cracks and voids in multiple layers of delicately laminated dololutite. Some curled slabs may be coated with cryptalgal laminae. A layer of storm-derived lutite rip-ups at the bottom of the image. Rowatt Fm. Belcher Islands. A modern analogue is shown below.Mangroves stabilizing shell banks (storm ridges) adjacent a tidal Inlet, Auckland HarbourThe New Zealand mangrove Avicennia marina fringing the upper limits of tidal flats, interwoven with patches of salt marsh dominated by Salicornia. Tidal flat sediment is a mix of fine-grained sand and mud. The ruffled surface of the flats is primarily the result of burrowing crabs. Hauraki Gulf, New Zealand.A dense tangle of stilt roots characteristic of the mangrove Rhizophora. Trees here are 4-5 m high. The sediment surface is littered with fallen leaves and branches. Some of the roots have encrusting barnacles. Florida Everglades.Everglades alligators, including the little guy on its parent’s head.Part of a Zostera marina meadow (seagrass) on sandy tidal flats, Savory Island, British Columbia. Seagrasses are flowering plants that pollinate underwater. They can form extensive meadows and support a huge shallow marine biota.
